Detecting the peak value
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From: john1987 on 29 Jul 2010 13:17 Hi, I built the circuit that can detect the peak of the 100KHz , 2 Volts peak to peak sine wave but its not accurate or may be not working right. The problems seem to be choosing the right R and C values. Is there any way that I can do this with out using a Capcitor and a resistor and if not than whats the best possible way to choose the R and C values. I do require the edge to occur as close as possible to the sine wave positive and negative peaks. I used Low Pass filter. you can find the diagram of the circuit and the waveform at the following links. http://a.imageshack.us/img651/6509/161617.jpg http://a.imageshack.us/img829/6505/161639.jpg Thanks John
From: Jim Thompson on 29 Jul 2010 14:05 On Thu, 29 Jul 2010 10:17:29 -0700 (PDT), john1987 <conphiloso(a)hotmail.com> wrote: >Hi, > >I built the circuit that can detect the peak of the 100KHz , 2 Volts >peak to peak sine wave but its not accurate or may be not working >right. >The problems seem to be choosing the right R and C values. Is there >any way that I can do this with out using a Capcitor and a resistor >and if not than whats the best possible way to choose the R and C >values. > >I do require the edge to occur as close as possible to the sine wave >positive and negative peaks. > >I used Low Pass filter. you can find the diagram of the circuit and >the waveform at the following links. > >http://a.imageshack.us/img651/6509/161617.jpg > >http://a.imageshack.us/img829/6505/161639.jpg > > > >Thanks >John That's not a peak detector, you're only comparing your signal to the "sorta-integral" of the signal. Surf on peak detector. There's many ways to do it, depending on your final needs... one-at-time or tracking. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Spice is like a sports car... Performance only as good as the person behind the wheel.
From: John Fields on 29 Jul 2010 14:27 On Thu, 29 Jul 2010 10:17:29 -0700 (PDT), john1987 <conphiloso(a)hotmail.com> wrote: >Hi, > >I built the circuit that can detect the peak of the 100KHz , 2 Volts >peak to peak sine wave but its not accurate or may be not working >right. >The problems seem to be choosing the right R and C values. Is there >any way that I can do this with out using a Capcitor and a resistor --- Yes, there are several. --- >and if not than whats the best possible way to choose the R and C >values. --- I wouldn't use the RC, I'd do it digitally. --- >I do require the edge to occur as close as possible to the sine wave >positive and negative peaks. --- How close is "as close as possible"? One degree? One millivolt?
From: Jim Thompson on 29 Jul 2010 15:00 On Thu, 29 Jul 2010 10:17:29 -0700 (PDT), john1987 <conphiloso(a)hotmail.com> wrote: >Hi, > >I built the circuit that can detect the peak of the 100KHz , 2 Volts >peak to peak sine wave but its not accurate or may be not working >right. >The problems seem to be choosing the right R and C values. Is there >any way that I can do this with out using a Capcitor and a resistor >and if not than whats the best possible way to choose the R and C >values. > >I do require the edge to occur as close as possible to the sine wave >positive and negative peaks. > >I used Low Pass filter. you can find the diagram of the circuit and >the waveform at the following links. > >http://a.imageshack.us/img651/6509/161617.jpg > >http://a.imageshack.us/img829/6505/161639.jpg > > > >Thanks >John Reading more carefully :-( You really are after a peak "finder". So use a differentiator and run the result thru a comparator... current in differentiating capacitor reverses at the peak. OR... If frequency is stable, use the all-pass I recently posted to get an accurate 90� phase shift, then thru a comparator. Fields idea sounds good too... I'm guessing use a tracking A-to-D and watch for count direction reversal?? ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Spice is like a sports car... Performance only as good as the person behind the wheel.
From: john1987 on 29 Jul 2010 15:01
Hi, Thanks for your response. I need analog or digital solution to implement it. I have doe search on peak detector on the internet and found many circuits. But I need something that can do what I mentioned in the diagram. Ideally with out those capacitor and resistor. If you can direct me in correct way than I wil be thankful. John |